[CVE-2026-74605][MODERATE 7.0] eventfs: Use children field for rcu head and add memory barriers

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-74605
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: eventfs: Use children field for rcu head and add memory barriers
Commit: 004f7232e49730448f91665e76bdd7dff8e0c638
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=004f7232e49730448f91665e76bdd7dff8e0c638
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74605
Analysis date: Sat, 22 Aug 2026 15:12:00 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
eventfs can race inode freeing with SRCU protected directory iteration, allowing the iterator to consume list storage that is being reused for an RCU callback, causing corrupt list traversal and a local kernel crash with weak UAF based privilege escalation concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74605 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74605

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-74605	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'eventfs can race inode freeing with SRCU protected directory iteration. The iterator may read the eventfs inode children list while the same storage is being reused for an RCU callback, which can make the next list pointer corrupt or refer to freed memory. This is a local race and UAF candidate in tracefs eventfs iteration rather than a packet or remote network issue. For the CVSS the PR:L means a local user or delegated tracing service account with access to tracefs eventfs paths may be able to participate in the triggering conditions. AC:H is used because successful triggering depends on a narrow timing window between free and iteration. Impact is at least local denial of service via kernel crash. In the paranoid interpretation, corrupt list traversal around a freed kernel object can justify C:H and I:H for manual review sensitivity, even though a stable privilege escalation primitive is not proven by the diff alone.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-74605 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	DISK INIT TRACE UAF LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local low privilege trigger: +1. A local process with access to tracefs or delegated tracing/eventfs access can participate in directory iteration paths.
* Memory corruption, weak or indirect corruption candidate: +1. The iterator can observe list storage that is being reused as an RCU callback field, producing a corrupt next pointer or invalid object interpretation.
* Real lifetime corruption: +1. This is an SRCU/RCU lifetime and object layout reuse issue around eventfs inode freeing.
* Reliable kernel crash / strong DoS: +1. Corrupt list traversal in kernel memory can realistically lead to an Oops, invalid dereference, or kernel crash.
* Hard or unreliable race: -1. Triggering depends on timing between eventfs inode free and SRCU protected iteration.

Paranoid additional interpretation:

* Weak LPE concern: +1. The bug involves stale or corrupt object traversal around freed kernel objects, but no controlled reclaim, overwrite, callback control, or stable replacement primitive is shown.
* Confidentiality impact plausible: +1. Only for paranoid triage, because corrupt list traversal may access unintended kernel objects.
* Integrity impact plausible: +1. Only for paranoid triage, because corrupt list traversal may affect object lifetime or traversal state.
* Race-UAF cap applied. This class is capped at 5 because the patch does not show attacker-controlled reclaim, write-after-free, type confusion, callback dispatch, or arbitrary write.

Call-site confidence: high. The patch includes both the freeing path and the SRCU iteration path.

## 3. Reachability analysis

This is a local tracefs/eventfs issue, not a network reachable vulnerability. A realistic trigger requires local interaction with tracefs eventfs paths and concurrent freeing of eventfs inodes, likely through tracing activity, module or event teardown, or a privileged tracing manager. In typical deployments, unrestricted tracefs manipulation is not available to ordinary users, but read or delegated tracing access may exist through tracing groups, service accounts, containers, or diagnostic tooling. Namespaces do not automatically make this remote, but delegated tracing access can reduce the practical privilege requirement from administrator to local low privilege.

## 4. Severity interpretation

This behaves above ordinary Moderate because it is an RCU/SRCU lifetime race with corrupt kernel list traversal. The realistic demonstrated impact is local DoS through kernel crash or invalid traversal. The theoretical memory corruption potential is higher, but the patch does not demonstrate a strong privilege escalation primitive such as controlled reclaim, controlled overwrite, refcount takeover, callback control, or arbitrary write. Therefore the conservative score remains borderline, while the paranoid score reaches Actionable Moderate and should not be auto-closed.

## 5. One-sentence report phrase

eventfs can race inode freeing with SRCU protected directory iteration, allowing the iterator to consume list storage that is being reused for an RCU callback, causing corrupt list traversal and a local kernel crash with weak UAF based privilege escalation concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. This is a local RCU/SRCU lifetime race with corrupt kernel object traversal, so it should receive manual review even though practical privilege escalation is not demonstrated.

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: eventfs: Use children field for rcu head and add memory barriers
Commit: 004f7232e49730448f91665e76bdd7dff8e0c638
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=004f7232e49730448f91665e76bdd7dff8e0c638

Commit description:

When an eventfs inode is freed, it sets ei->is_freed and then uses its
ei->list to add it to the srcu link list as the list field is a union with
the rcu list head. As the ei->list is used to iterate over an SRCU
protected list without taking the eventfs_mutex, there's nothing stopping
the iteration over that list to see the ei->rcu instead of the ei->list
and it will read a corrupt target.

To fix this, change the union of the rcu list head with the children list.
On freeing the eventfs inode, set the is_free and execute a smp_wmb()
before adding the eventfs inode to the SRCU list.

On iteration of the ei->children list, at the start, execute a smp_rmb()
and then read the is_freed of the ei to see if the children list is still
valid. If is_freed is set, then the ei_child read is not valid and the
loop should exit immediately.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260808094215.4252430d@robin
Fixes: 704f960 ("eventfs: Read ei->entries before ei->children in eventfs_iterate()")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260806022719.375354-1-shuangpeng.kernel%40gmail.com
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/tracefs/event_inode.c
  fs/tracefs/internal.h

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=004f7232e49730448f91665e76bdd7dff8e0c638

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-74605 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74605

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 3
  Paranoid ActionableScore: 5

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).